(1) Field of the Invention
This invention relates to a linear ball bearing unit for guiding a linear movement of a machine by rolling friction with a reduced resistance to movement. More particularly, the invention concerns a linear ball bearing unit useful on slide surfaces of table saddles or machining centers of machine tools or in reciprocating sections of transfer devices which carry a weight.
(2) Description of Prior Art
The linear bearings currently in general use are of ball-push type which is capable of supporting vertical loads but can carry only a fraction of moment or upward loads.
On the other hand, a track shaft with a four-directional load-carrying bearing, disclosed in Japanese Patent Publication No. 52-43973, can take only 0.43 of upward load and 0.5 of lateral loads as compared with a rating 1 for the vertical load on the top surface.
However, the upward loads occur in extremely large magnitudes in industrial applications, and, since this problem cannot be solved by the four-directional load-carrying bearings, there often arises a necessity for an unduly large-sized bearing or a bearing of a shape which is difficult to adopt from the standpoint of designing.
Moreover, for adjusting clearance in the conventional bearings of this class, an outer cylinder is inserted into the bearing case which is provided with a slotted groove. The insertion of the outer cylinder fails to make accurate adjustment of clearance due to the existence of a fine clearance between the outer cylinder and the bearing case, and to account for the variation in height which is caused upon imposing a load.